In EU, there's an unspoken rule for cars to report speeds inflated by 5%.

This is possibly based on an old research of SAAB which used a reverse logarithmic speedometer, giving feeling of exaggerated acceleration until 120-130 KM/h or so. Then the scale tightened so much that going significantly faster didn't move the speedometer that much. Also the needle hit top left quadrant much faster, hinting that you're going really fast.

Also, EU uses L/100KM concept instead of MPG. When the speed is 0, most cars switch to L/h scale. Toyotas also show an infinity symbol when in MPG mode while the speed is 0.

For anyone interested below are some examples:

1- https://upload.wikimedia.org/wikipedia/commons/5/5c/Instrume...

2- https://i.ytimg.com/vi/V0RyHPM0mBI/maxresdefault.jpg

I remember the numbers right, but it wasn't reverse logarithmic scale. It was a hard transition at 140KM/h.

Are you sure they displayed mpg and not l/100km?

Dashboards are user or factory configurable. Our Ford Focus had a button to change between L/100KM and MPG.

My friend's VW Bora's dashboard was OBDII configurable. The options were Japan/US/EU IIRC. Setting to US not only changed it to MPG scale, enabled the door-open beeps. :D

Well, I wouldn't be surprised if the software internally always computed l/100km and the converted to mpg for display.

It's much more direct for car to measure consumption as L/100KM. However the conversion is done by the instrument cluster on the VW. We were connecting to the instrument cluster via CANBUS and changing the setting directly on it. Also the beeps were handled at the cluster, not at the central config.

Car technology is weird...

The car manufacturers always make their speedometers show a little bit too much (like 10%) to make sure they never show too little (or they would get sued badly and get their cars taken of the streets). We _accept_ that the car companies do this for legal/security reasons, which is very different from _wanting_ them to do it. I would be angry if they did the same if the fuel indicator.

No they don’t. I have a 2005 ford with a speedometer that matches GPS all of the way up to 85 mph (haven’t tested higher).

I had a 1996 Ford Mondeo that showed 10% more. Then I had 2004 Ford Mondeo and it was 5% more. I sold that one and bought a 2008 Ford Mondeo and it is 5% more. My other car - 1998 Ford Fiesta - is 10% more. I also drove a 2011 Ford Mondeo and it showed more but I hadn't had it long enough to care to calculate how much exactly.

I tested all the cars except the Fiesta up to 230 km/h and the 2008 one up to 260 km/h (it's the 2.5T).

All the cars are/were German except for the Fiesta, that one is Czech.

Maybe it’s something they do in Europe but not the US.

Maybe your car GPS is reporting higher? All cars I've driven were reporting %5-%10 more.

It’s not a car gps. It’s a receiver on a phone. That can’t be wrong by that much or the position would be wrong.

Japanese customers, too. Back in the day, there was a gentleman's agreement among Japanese automakers to limit power output of JDM cars to 276 hp.

In reality, Japanese performance cars were all spectacularly underrated. Your "276 hp" sports coupe is probably making 350 hp. It was more of a gentleman's agreement to lie about power figures than anything else.